Simplified merge list construction for small coding blocks

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes processing circuitry. The processing circuitry decodes prediction information for a current block in a current picture. The processing circuitry determines whether an area of the current block is smaller than or equal to a threshold. The processing circuitry constructs a motion vector predictor list including a number of motion vector predictors. The number of motion vector predictors is based on whether the area of the current block is determined to be smaller than or equal to the threshold. The processing circuitry reconstructs the current block based on the motion vector predictor list.

INCORPORATION BY REFERENCE

This application claims the benefit of priority to U.S. Provisional Application No. 62/777,735, “SIMPLIFIED MERGE LIST CONSTRUCTION FOR SMALL CODING BLOCKS” filed on Dec. 10, 2018, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to video coding.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Video coding and decoding can be performed using inter-picture prediction with motion compensation. Uncompressed digital video can include a series of pictures, each picture having a spatial dimension of, for example, 1920×1080 luminance samples and associated chrominance samples. The series of pictures can have a fixed or variable picture rate (informally also known as frame rate) of, for example, 60 pictures per second or 60 Hz. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video at 8 bit per sample (1920×1080 luminance sample resolution at 60 Hz frame rate) requires close to 1.5 Gbit/s bandwidth. An hour of such video requires more than 600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction of redundancy in the input video signal, through compression. Compression can help reduce the aforementioned bandwidth or storage space requirements, in some cases by two orders of magnitude or more. Both lossless and lossy compression, as well as a combination thereof can be employed. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between original and reconstructed signals is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely employed. The amount of distortion tolerated depends on the application; for example, users of certain consumer streaming applications may tolerate higher distortion than users of television distribution applications. The compression ratio achievable can reflect that: higher allowable/tolerable distortion can yield higher compression ratios.

A video encoder and decoder can utilize techniques from several broad categories, including, for example, motion compensation, transform, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding. In intra coding, sample values are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, the picture is spatially subdivided into blocks of samples. When all blocks of samples are coded in intra mode, that picture can be an intra picture. Intra pictures and their derivations such as independent decoder refresh pictures, can be used to reset the decoder state and can, therefore, be used as the first picture in a coded video bitstream and a video session, or as a still image. The samples of an intra block can be exposed to a transform, and the transform coefficients can be quantized before entropy coding. Intra prediction can be a technique that minimizes sample values in the pre-transform domain. In some cases, the smaller the DC value after a transform is, and the smaller the AC coefficients are, the fewer the bits that are required at a given quantization step size to represent the block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2 generation coding technologies, does not use intra prediction. However, some newer video compression technologies include techniques that attempt, from, for example, surrounding sample data and/or metadata obtained during the encoding/decoding of spatially neighboring, and preceding in decoding order, blocks of data. Such techniques are henceforth called “intra prediction” techniques. Note that in at least some cases, intra prediction is only using reference data from the current picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more than one of such techniques can be used in a given video coding technology, the technique in use can be coded in an intra prediction mode. In certain cases, modes can have submodes and/or parameters, and those can be coded individually or included in the mode codeword. Which codeword to use for a given mode/submode/parameter combination can have an impact in the coding efficiency gain through intra prediction, and so can the entropy coding technology used to translate the codewords into a bitstream.

A certain mode of intra prediction was introduced with H.264, refined in H.265, and further refined in newer coding technologies such as joint exploration model (JEM), versatile video coding (VVC), and benchmark set (BMS). A predictor block can be formed using neighboring sample values belonging to already available samples. Sample values of neighboring samples are copied into the predictor block according to a direction. A reference to the direction in use can be coded in the bitstream or may be predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of nine predictor directions known from H.265's 33 possible predictor directions (corresponding to the 33 angular modes of the 35 intra modes). The point where the arrows converge (101) represents the sample being predicted. The arrows represent the direction from which the sample is being predicted. For example, arrow (102) indicates that sample (101) is predicted from a sample or samples to the upper right, at a 45 degree angle from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from a sample or samples to the lower left of sample (101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a square block (104) of 4×4 samples (indicated by a dashed, boldface line). The square block (104) includes 16 samples. Each sample is labelled with an “S”, its position in the Y dimension (e.g., row index), and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample in the Y dimension (from the top) and the first (from the left) sample in the X dimension. Similarly, sample S44 is the fourth sample in block (104) in both the Y and X dimensions. As the block is 4×4 samples in size, S44 is at the bottom right. Further shown are reference samples that follow a similar numbering scheme. A reference sample is labelled with an R, its Y position (e.g., row index) and X position (column index) relative to block (104). In both H.264 and H.265, prediction samples neighbor the block under reconstruction; therefore no negative values need to be used.

Intra picture prediction can work by copying reference sample values from the neighboring samples as appropriated by the signaled prediction direction. For example, assume the coded video bitstream includes signaling that, for this block, indicates a prediction direction consistent with arrow (102)—that is, samples are predicted from a prediction sample or samples to the upper right, at a 45 degree angle from the horizontal. In that case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Sample S44 is then predicted from reference sample R08.

In certain cases, the values of multiple reference samples may be combined, for example through interpolation, in order to calculate a reference sample; especially when the directions are not evenly divisible by 45 degrees.

The number of possible directions has increased as video coding technology has developed. In H.264 (year 2003), nine different direction could be represented. That increased to 33 in H.265 (year 2013), and JEMNVC/BMS, at the time of disclosure, can support up to 65 directions. Experiments have been conducted to identify the most likely directions, and certain techniques in the entropy coding are used to represent those likely directions in a small number of bits, accepting a certain penalty for less likely directions. Further, the directions themselves can sometimes be predicted from neighboring directions used in neighboring, already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra prediction directions according to JEM to illustrate the increasing number of prediction directions over time.

The mapping of intra prediction directions bits in the coded video bitstream that represent the direction can be different from video coding technology to video coding technology; and can range, for example, from simple direct mappings of prediction direction to intra prediction mode, to codewords, to complex adaptive schemes involving most probable modes, and similar techniques. In all cases, however, there can be certain directions that are statistically less likely to occur in video content than certain other directions. As the goal of video compression is the reduction of redundancy, those less likely directions will, in a well working video coding technology, be represented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relate to techniques where a block of sample data from a previously reconstructed picture or part thereof (reference picture), after being spatially shifted in a direction indicated by a motion vector (MV henceforth), is used for the prediction of a newly reconstructed picture or picture part. In some cases, the reference picture can be the same as the picture currently under reconstruction. MVs can have two dimensions X and Y, or three dimensions, the third being an indication of the reference picture in use (the latter, indirectly, can be a time dimension).

In some video compression techniques, an MV applicable to a certain area of sample data can be predicted from other MVs, for example from those related to another area of sample data spatially adjacent to the area under reconstruction, and preceding that MV in decoding order. Doing so can substantially reduce the amount of data required for coding the MV, thereby removing redundancy and increasing compression. MV prediction can work effectively, for example, because when coding an input video signal derived from a camera (known as natural video) there is a statistical likelihood that areas larger than the area to which a single MV is applicable move in a similar direction and, therefore, can in some cases be predicted using a similar motion vector derived from MVs of neighboring areas. That results in the MV found for a given area to be similar or the same as the MV predicted from the surrounding MVs, and that in turn can be represented, after entropy coding, in a smaller number of bits than what would be used if coding the MV directly. In some cases, MV prediction can be an example of lossless compression of a signal (namely: the MVs) derived from the original signal (namely: the sample stream). In other cases, MV prediction itself can be lossy, for example because of rounding errors when calculating a predictor from several surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec. H.265, “High Efficiency Video Coding”, December 2016). Out of the many MV prediction mechanisms that H.265 offers, advanced motion vector prediction (AMVP) mode and merge mode are described here.

In AMVP mode, motion information of spatial and temporal neighboring blocks of a current block can be used to predict motion information of the current block, while the prediction residue is further coded. Examples of spatial and temporal neighboring candidates are shown in FIG. 1C and FIG. 1D, respectively. A two-candidate motion vector predictor list is formed. The first candidate predictor is from the first available motion vector of the two blocks A0 (112), A1 (113) at the bottom-left corner of the current block (111), as shown in FIG. 1C. The second candidate predictor is from the first available motion vector of the three blocks B0 (114), B1 (115), and B2 (116) above the current block (111). If no valid motion vector can be found from the checked locations, no candidate will be filled in the list. If two available candidates have the same motion information, only one candidate will be kept in the list. If the list is not full, i.e., the list does not have two different candidates, a temporal co-located motion vector (after scaling) from C0 (122) at the bottom-right corner of a co-located block (121) in a reference picture will be used as another candidate, as shown in FIG. 1D. If motion information at C0 (122) location is not available, the center location C1 (123) of the co-located block in the reference picture will be used instead. In the above derivation, if there are still not enough motion vector predictor candidates, a zero motion vector will be used to fill up the list. Two flags mvp_l0_flag and mvp_l1_flag are signaled in the bitstream to indicate the AMVP index (0 or 1) for MV candidate list L0 and L1, respectively.

In a merge mode for inter-picture prediction, if a merge flag (including a skip flag) is signaled as TRUE, a merge index is then signaled to indicate which candidate in a merge candidate list will be used to indicate the motion vectors of the current block. At the decoder, the merge candidate list is constructed based on spatial and temporal neighbors of the current block. As shown in FIG. 1C, up to four MVs derived from five spatial neighboring blocks (A0-B2) are added into the merge candidate list. In addition, as shown in FIG. 1D, up to one MV from two temporal co-located blocks (C0 and C1) in the reference picture is added to the list. Additional merge candidates include combined bi-predictive candidates and zero motion vector candidates. Before taking the motion information of a block as a merge candidate, redundancy checks are performed to check whether it is identical to an element in the current merge candidate list. If it is different from each element in the current merge candidate list, it will be added to the merge candidate list as a merge candidate. MaxMergeCandsNum is defined as the size of the merge candidate list in terms of candidate number. In HEVC, MaxMergeCandsNum is signaled in the bitstream. A skip mode can be considered as a special merge mode with zero residual.

In VVC, a sub-block based temporal motion vector prediction (SbTMVP) method, similar to the temporal motion vector prediction (TMVP) in HEVC, can use the motion field in the collocated picture to improve motion vector prediction and merge mode for CUs in the current picture. The same collocated picture used by TMVP is used for SbTVMP. SbTMVP differs from TMVP in the following two main aspects: (1) TMVP predicts motion at CU level but SbTMVP predicts motion at sub-CU level; and (2) whereas TMVP fetches the temporal motion vectors from the collocated block in the collocated picture (the collocated block is the bottom-right or center block relative to the current CU), SbTMVP applies a motion shift before fetching the temporal motion information from the collocated picture, where the motion shift is obtained from the motion vector from one of the spatial neighboring blocks of the current CU.

The SbTVMP process is illustrated in FIG. 1E and FIG. 1F. SbTMVP predicts the motion vectors of the sub-CUs within the current CU in two steps. In the first step, as shown in FIG. 1E, the spatial neighbors of a current block (131) are examined in the order of A1 (132), B1 (133), B0 (134), and A0 (135). Once the first available spatial neighboring block that has a motion vector that uses the collocated picture as its reference picture is identified, this motion vector is selected to be the motion shift to be applied. If no such motion vector is identified from the spatial neighbors, then the motion shift is set to (0, 0).

In the second step, the motion shift identified in the first step is applied (i.e., added to the coordinates of the current block) to obtain sub-CU-level motion information (e.g., motion vectors and reference indices) from the collocated picture as shown in FIG. 1F. The example in FIG. 1F assumes the motion shift (149) is set to the motion vector of the spatial neighboring block A1 (143). Then, for a current sub-CU (e.g., sub-CU (144)) in the current block (142) of the current picture (141), the motion information of a corresponding collocated sub-CU (e.g., collocated sub-CU (154)) in the collocated block (152) of the collocated picture (151) is used to derive the motion information for the current sub-CU. The motion information of the corresponding collocated sub-CU (e.g., collocated sub-CU (154)) is converted to the motion vectors and reference indices of the current sub-CU (e.g., sub-CU (144)) in a similar way as the TMVP process in HEVC, where temporal motion scaling is applied to align the reference pictures of the temporal motion vectors to the reference picture of the current CU.

In VVC, a combined sub-block based merge list which contains both a SbTVMP candidate and affine merge candidates can be used in sub-block based merge mode. The SbTVMP mode is enabled/disabled by a sequence parameter set (SPS) flag. If the SbTMVP mode is enabled, the SbTMVP predictor is added as the first entry of the sub-block based merge list, and followed by the affine merge candidates. The maximum allowed size of the sub-block based merge list is 5 in some applications. The sub-CU size used in SbTMVP is fixed to be 8×8, for example. As done for affine merge mode, SbTMVP mode is only applicable to a CU when both width and height are larger than or equal to 8.

The encoding logic of an additional SbTMVP merge candidate is the same as the encoding logic for other merge candidates. That is, for each CU in a P or B slice, an additional rate distortion (RD) check is performed to decide whether to use the SbTMVP candidate.

In VVC, a history-based MVP (HMVP) method includes a HMVP candidate that is defined as the motion information of a previously coded block. A table with multiple HMVP candidates is maintained during the encoding/decoding process. The table is emptied when a new slice is encountered. Whenever there is an inter-coded non-affine block, the associated motion information is added to the last entry of the table as a new HMVP candidate. The coding flow of the HMVP method is depicted in FIG. 1G.

The table size S is set to be 6, which indicates up to 6 HMVP candidates may be added to the table. When inserting a new motion candidate into the table, a constrained FIFO rule is utilized such that a redundancy check is first applied to determine whether an identical HMVP is in the table. If found, the identical HMVP is removed from the table and all the HMVP candidates afterwards are moved forward, i.e., with indices reduced by 1. FIG. 1H shows an example of inserting a new motion candidate into the HMVP table.

HMVP candidates could be used in the merge candidate list construction process. The latest several HMVP candidates in the table are checked in order and inserted into the candidate list after the TMVP candidate. Pruning is applied on the HMVP candidates to the spatial or temporal merge candidate excluding sub-block motion candidate (i.e., ATMVP).

To reduce the number of pruning operations, the number of HMVP candidates to be checked (denoted by L) is set as L=(N<=4)? M: (8−N), where N indicates a number of available non-sub-block merge candidates and M indicates a number of available HMVP candidates in the table. In addition, once the total number of available merge candidates reaches the signaled maximally allowed merge candidates minus 1, the merge candidate list construction process from the HMVP list is terminated. Moreover, the number of pairs for combined bi-predictive merge candidate derivation is reduced from 12 to 6.

HMVP candidates could also be used in the AMVP candidate list construction process. The motion vectors of the last K HMVP candidates in the table are inserted after the TMVP candidate. Only HMVP candidates with the same reference picture as the AMVP target reference picture are used to construct the AMVP candidate list. Pruning is applied on the HMVP candidates. In some applications, K is set to 4 while the AMVP list size is kept unchanged, i.e., equal to 2.

Pairwise average candidates are generated by averaging predefined pairs of candidates in the current merge candidate list. In VVC, the number of pairwise average candidates is 6, and the predefined pairs are defined as {(0, 1), (0, 2), (1, 2), (0, 3), (1, 3), (2, 3)}, where the numbers denote the merge indices to the merge candidate list. The averaged motion vectors are calculated separately for each reference list. If both motion vectors are available in one list, these two motion vectors are averaged even when they point to different reference pictures. If only one motion vector is available, the one motion vector is directly used. If no motion vector is available, this list is considered as invalid. The pairwise average candidates can replace the combined candidates in the HEVC standard.

Multi-hypothesis prediction can be applied to improve uni-prediction of AMVP mode. One flag is signaled to enable or disable multi-hypothesis prediction. Moreover, one additional merge index is signaled when the flag is true. In this way, multi-hypothesis prediction turns uni-prediction into bi-prediction, where one prediction is acquired using the original syntax elements in AMVP mode while the other prediction is acquired using the merge mode. The final prediction uses 1:1 weights to combine these two predictions as in bi-prediction. The merge candidate list is first derived from merge mode with sub-CU candidates (e.g., affine, alternative temporal motion vector prediction (ATMVP)) excluded. Next, the merge candidate list is separated into two individual lists, one for list 0 (L0) containing all L0 motions from the candidates, and the other for list 1 (L1) containing all L1 motions. After removing redundancy and filling vacancy, two merge lists are generated for L0 and L1, respectively. There are two constraints when applying multi-hypothesis prediction for improving AMVP mode. First, it is enabled for those CUs with the luma coding block (CB) area larger than or equal to 64. Second, it is only applied to L1 for low delay B pictures.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry.

The processing circuitry decodes prediction information for a current block in a current picture that is a part of a coded video sequence. The processing circuitry determines whether an area of the current block is smaller than or equal to a threshold. The processing circuitry constructs a motion vector predictor list including a number of motion vector predictors. The number of motion vector predictors is based on whether the area of the current block is determined to be smaller than or equal to the threshold. The processing circuitry reconstructs the current block based on the motion vector predictor list.

According to aspects of the disclosure, the number of motion vector predictors included in the motion vector predictor list is a first number when the area of the current block is determined to be smaller than or equal to the threshold, and the number of motion vector predictors included in the motion vector predictor list is a second number that is larger than the first number when the area of the current block is determined to be larger than the threshold.

According to aspects of the disclosure, the prediction information indicates the current block is to be further partitioned into a plurality of smaller blocks. The processing circuitry partitions the current block into the plurality of smaller blocks. The processing circuitry determines whether an area of one of the plurality of smaller blocks is smaller than or equal to the threshold. The processing circuitry constructs the motion vector predictor list based on whether the area of the one of the plurality of smaller blocks is determined to be smaller than or equal to the threshold. The number of motion vector predictors included in the motion vector predictor list is the first number when the area of the one of the plurality of smaller blocks is determined to be smaller than or equal to the threshold, and the number of motion vector predictors included in the motion vector predictor list is the second number when the area of the one of the plurality of smaller blocks is determined to be larger than the threshold.

According to aspects of the disclosure, the prediction information indicates a partition size of the current block. The processing circuitry determines whether the partition size is smaller than or equal to the threshold. The processing circuitry constructs the motion vector predictor list based on whether the partition size is determined to be smaller than or equal to the threshold. The number of motion vector predictors included in the motion vector predictor list is the first number when the partition size is determined to be smaller than or equal to the threshold, and the number of motion vector predictors included in the motion vector predictor list is the second number when the partition size is determined to be larger than the threshold.

In an embodiment, the threshold is a preset number of luma samples.

In an embodiment, the threshold corresponds to a picture resolution of the current picture.

In an embodiment, the threshold is signaled in the coded video sequence.

In an embodiment, the motion vector predictor list including the first number of motion vector predictors is constructed based on a first set of spatial or temporal motion vector predictors. The first set of spatial or temporal motion vector predictors is smaller than a second set of spatial or temporal motion vector predictors used to construct the motion vector predictor list including the second number of motion vector predictors.

In an embodiment, the motion vector predictor list including the first number of motion vector predictors does not include any spatial or temporal motion vector predictors.

In an embodiment, a first number of redundancy checks is performed to construct the motion vector predictor list including the first number of motion vector predictors, and a second number of redundancy checks is performed to construct the motion vector predictor list including the second number of motion vector predictors. The first number of redundancy checks is less than the second number of redundancy checks.

In an embodiment, the first number of redundancy checks does not include at least one of a comparison between (i) a possible spatial motion vector predictor and a first existing spatial motion vector predictor in the motion vector predictor list, (ii) a possible temporal motion vector predictor and a first existing temporal motion vector predictor in the motion vector predictor list, (iii) a possible history-based motion vector predictor and the first or another existing spatial motion vector predictor in the motion vector predictor list, and (iv) the possible history-based motion vector predictor and the first or another existing temporal motion vector predictor in the motion vector predictor list.

In an embodiment, the motion vector predictor list including the first number of motion vector predictors is constructed without any redundancy check.

In an embodiment, at least one of the motion vector predictors uses the current picture as a reference picture such that a reference block of the at least one of the motion vector predictors is within the current picture.

Aspects of the disclosure also provide a non-transitory computer-readable medium storing instructions which when executed by a computer for video decoding cause the computer to perform any one or a combination of the methods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosed subject matter will be more apparent from the following detailed description and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intra prediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 1C is a schematic illustration of a current block and its surrounding spatial merge candidates in one example.

FIG. 1D is a schematic illustration of a co-located block and temporal merge candidates in one example.

FIG. 1E is a schematic illustration of a current block and its surrounding spatial merge candidates for sub-block based temporal motion vector prediction (SbTMVP) according to one example.

FIG. 1F is an exemplary process of deriving SbTMVP candidates according to one example.

FIG. 1G is a decoding flow of a history based motion vector prediction (HMVP) method in one example.

FIG. 1H is an exemplary process of updating a table in HMVP according to one example.

FIG. 2 is a schematic illustration of a simplified block diagram of a communication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of a communication system in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of a decoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of an encoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with another embodiment.

FIG. 7 shows a block diagram of a decoder in accordance with another embodiment.

FIG. 8 shows a flowchart outlining an exemplary process according to some embodiments of the disclosure.

FIG. 9 shows another flowchart outlining an exemplary process according to some embodiments of the disclosure.

FIG. 10 is a schematic illustration of a computer system in accordance with an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system (200) according to an embodiment of the present disclosure. The communication system (200) includes a plurality of terminal devices that can communicate with each other, via, for example, a network (250). For example, the communication system (200) includes a first pair of terminal devices (210) and (220) interconnected via the network (250). In the FIG. 2 example, the first pair of terminal devices (210) and (220) performs unidirectional transmission of data. For example, the terminal device (210) may code video data (e.g., a stream of video pictures that are captured by the terminal device (210)) for transmission to the other terminal device (220) via the network (250). The encoded video data can be transmitted in the form of one or more coded video bitstreams. The terminal device (220) may receive the coded video data from the network (250), decode the coded video data to recover the video pictures and display video pictures according to the recovered video data. Unidirectional data transmission may be common in media serving applications and the like.

In another example, the communication system (200) includes a second pair of terminal devices (230) and (240) that performs bidirectional transmission of coded video data that may occur, for example, during videoconferencing. For bidirectional transmission of data, in an example, each terminal device of the terminal devices (230) and (240) may code video data (e.g., a stream of video pictures that are captured by the terminal device) for transmission to the other terminal device of the terminal devices (230) and (240) via the network (250). Each terminal device of the terminal devices (230) and (240) also may receive the coded video data transmitted by the other terminal device of the terminal devices (230) and (240), and may decode the coded video data to recover the video pictures and may display video pictures at an accessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and (240) may be illustrated as servers, personal computers and smart phones but the principles of the present disclosure may be not so limited. Embodiments of the present disclosure find application with laptop computers, tablet computers, media players and/or dedicated video conferencing equipment. The network (250) represents any number of networks that convey coded video data among the terminal devices (210), (220), (230) and (240), including for example wireline (wired) and/or wireless communication networks. The communication network (250) may exchange data in circuit-switched and/or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks and/or the Internet. For the purposes of the present discussion, the architecture and topology of the network (250) may be immaterial to the operation of the present disclosure unless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosed subject matter, the placement of a video encoder and a video decoder in a streaming environment. The disclosed subject matter can be equally applicable to other video enabled applications, including, for example, video conferencing, digital TV, storing of compressed video on digital media including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that can include a video source (301), for example a digital camera, creating for example a stream of video pictures (302) that are uncompressed. In an example, the stream of video pictures (302) includes samples that are taken by the digital camera. The stream of video pictures (302), depicted as a bold line to emphasize a high data volume when compared to encoded video data (304) (or coded video bitstreams), can be processed by an electronic device (320) that includes a video encoder (303) coupled to the video source (301). The video encoder (303) can include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter as described in more detail below. The encoded video data (304) (or encoded video bitstream (304)), depicted as a thin line to emphasize the lower data volume when compared to the stream of video pictures (302), can be stored on a streaming server (305) for future use. One or more streaming client subsystems, such as client subsystems (306) and (308) in FIG. 3 can access the streaming server (305) to retrieve copies (307) and (309) of the encoded video data (304). A client subsystem (306) can include a video decoder (310), for example, in an electronic device (330). The video decoder (310) decodes the incoming copy (307) of the encoded video data and creates an outgoing stream of video pictures (311) that can be rendered on a display (312) (e.g., display screen) or other rendering device (not depicted). In some streaming systems, the encoded video data (304), (307), and (309) (e.g., video bitstreams) can be encoded according to certain video coding/compression standards. Examples of those standards include ITU-T Recommendation H.265. In an example, a video coding standard under development is informally known as VVC. The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can include other components (not shown). For example, the electronic device (320) can include a video decoder (not shown) and the electronic device (330) can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to an embodiment of the present disclosure. The video decoder (410) can be included in an electronic device (430). The electronic device (430) can include a receiver (431) (e.g., receiving circuitry). The video decoder (410) can be used in the place of the video decoder (310) in the FIG. 3 example.

The receiver (431) may receive one or more coded video sequences to be decoded by the video decoder (410); in the same or another embodiment, one coded video sequence at a time, where the decoding of each coded video sequence is independent from other coded video sequences. The coded video sequence may be received from a channel (401), which may be a hardware/software link to a storage device which stores the encoded video data. The receiver (431) may receive the encoded video data with other data, for example, coded audio data and/or ancillary data streams, that may be forwarded to their respective using entities (not depicted). The receiver (431) may separate the coded video sequence from the other data. To combat network jitter, a buffer memory (415) may be coupled in between the receiver (431) and an entropy decoder/parser (420) (“parser (420)” henceforth). In certain applications, the buffer memory (415) is part of the video decoder (410). In others, it can be outside of the video decoder (410) (not depicted). In still others, there can be a buffer memory (not depicted) outside of the video decoder (410), for example to combat network jitter, and in addition another buffer memory (415) inside the video decoder (410), for example to handle playout timing. When the receiver (431) is receiving data from a store/forward device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (415) may not be needed, or can be small. For use on best effort packet networks such as the Internet, the buffer memory (415) may be required, can be comparatively large and can be advantageously of adaptive size, and may at least partially be implemented in an operating system or similar elements (not depicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstruct symbols (421) from the coded video sequence. Categories of those symbols include information used to manage operation of the video decoder (410), and potentially information to control a rendering device such as a render device (412) (e.g., a display screen) that is not an integral part of the electronic device (430) but can be coupled to the electronic device (430), as was shown in FIG. 4. The control information for the rendering device(s) may be in the form of Supplemental Enhancement Information (SEI messages) or Video Usability Information (VUI) parameter set fragments (not depicted). The parser (420) may parse/entropy-decode the coded video sequence that is received. The coding of the coded video sequence can be in accordance with a video coding technology or standard, and can follow various principles, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, and so forth. The parser (420) may extract from the coded video sequence, a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder, based upon at least one parameter corresponding to the group. Subgroups can include Groups of Pictures (GOPs), pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) and so forth. The parser (420) may also extract from the coded video sequence information such as transform coefficients, quantizer parameter values, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation on the video sequence received from the buffer memory (415), so as to create symbols (421).

Reconstruction of the symbols (421) can involve multiple different units depending on the type of the coded video picture or parts thereof (such as: inter and intra picture, inter and intra block), and other factors. Which units are involved, and how, can be controlled by the subgroup control information that was parsed from the coded video sequence by the parser (420). The flow of such subgroup control information between the parser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410) can be conceptually subdivided into a number of functional units as described below. In a practical implementation operating under commercial constraints, many of these units interact closely with each other and can, at least partly, be integrated into each other. However, for the purpose of describing the disclosed subject matter, the conceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). The scaler/inverse transform unit (451) receives a quantized transform coefficient as well as control information, including which transform to use, block size, quantization factor, quantization scaling matrices, etc. as symbol(s) (421) from the parser (420). The scaler/inverse transform unit (451) can output blocks comprising sample values that can be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451) can pertain to an intra coded block; that is: a block that is not using predictive information from previously reconstructed pictures, but can use predictive information from previously reconstructed parts of the current picture. Such predictive information can be provided by an intra picture prediction unit (452). In some cases, the intra picture prediction unit (452) generates a block of the same size and shape of the block under reconstruction, using surrounding already reconstructed information fetched from the current picture buffer (458). The current picture buffer (458) buffers, for example, partly reconstructed current picture and/or fully reconstructed current picture. The aggregator (455), in some cases, adds, on a per sample basis, the prediction information that the intra prediction unit (452) has generated to the output sample information as provided by the scaler/inverse transform unit (451).

In other cases, the output samples of the scaler/inverse transform unit (451) can pertain to an inter coded, and potentially motion compensated block. In such a case, a motion compensation prediction unit (453) can access reference picture memory (457) to fetch samples used for prediction. After motion compensating the fetched samples in accordance with the symbols (421) pertaining to the block, these samples can be added by the aggregator (455) to the output of the scaler/inverse transform unit (451) (in this case called the residual samples or residual signal) so as to generate output sample information. The addresses within the reference picture memory (457) from where the motion compensation prediction unit (453) fetches prediction samples can be controlled by motion vectors, available to the motion compensation prediction unit (453) in the form of symbols (421) that can have, for example X, Y, and reference picture components. Motion compensation also can include interpolation of sample values as fetched from the reference picture memory (457) when sub-sample exact motion vectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to various loop filtering techniques in the loop filter unit (456). Video compression technologies can include in-loop filter technologies that are controlled by parameters included in the coded video sequence (also referred to as coded video bitstream) and made available to the loop filter unit (456) as symbols (421) from the parser (420), but can also be responsive to meta-information obtained during the decoding of previous (in decoding order) parts of the coded picture or coded video sequence, as well as responsive to previously reconstructed and loop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that can be output to the render device (412) as well as stored in the reference picture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used as reference pictures for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture has been identified as a reference picture (by, for example, the parser (420)), the current picture buffer (458) can become a part of the reference picture memory (457), and a fresh current picture buffer can be reallocated before commencing the reconstruction of the following coded picture.

The video decoder (410) may perform decoding operations according to a predetermined video compression technology in a standard, such as ITU-T Rec. H.265. The coded video sequence may conform to a syntax specified by the video compression technology or standard being used, in the sense that the coded video sequence adheres to both the syntax of the video compression technology or standard and the profiles as documented in the video compression technology or standard. Specifically, a profile can select certain tools as the only tools available for use under that profile from all the tools available in the video compression technology or standard. Also necessary for compliance can be that the complexity of the coded video sequence is within bounds as defined by the level of the video compression technology or standard. In some cases, levels restrict the maximum picture size, maximum frame rate, maximum reconstruction sample rate (measured in, for example megasamples per second), maximum reference picture size, and so on. Limits set by levels can, in some cases, be further restricted through Hypothetical Reference Decoder (HRD) specifications and metadata for HRD buffer management signaled in the coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant) data with the encoded video. The additional data may be included as part of the coded video sequence(s). The additional data may be used by the video decoder (410) to properly decode the data and/or to more accurately reconstruct the original video data. Additional data can be in the form of, for example, temporal, spatial, or signal noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to an embodiment of the present disclosure. The video encoder (503) is included in an electronic device (520). The electronic device (520) includes a transmitter (540) (e.g., transmitting circuitry). The video encoder (503) can be used in the place of the video encoder (303) in the FIG. 3 example.

The video encoder (503) may receive video samples from a video source (501) (that is not part of the electronic device (520) in the FIG. 5 example) that may capture video image(s) to be coded by the video encoder (503). In another example, the video source (501) is a part of the electronic device (520).

The video source (501) may provide the source video sequence to be coded by the video encoder (503) in the form of a digital video sample stream that can be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ), and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). In a media serving system, the video source (501) may be a storage device storing previously prepared video. In a videoconferencing system, the video source (501) may be a camera that captures local image information as a video sequence. Video data may be provided as a plurality of individual pictures that impart motion when viewed in sequence. The pictures themselves may be organized as a spatial array of pixels, wherein each pixel can comprise one or more samples depending on the sampling structure, color space, etc. in use. A person skilled in the art can readily understand the relationship between pixels and samples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code and compress the pictures of the source video sequence into a coded video sequence (543) in real time or under any other time constraints as required by the application. Enforcing appropriate coding speed is one function of a controller (550). In some embodiments, the controller (550) controls other functional units as described below and is functionally coupled to the other functional units. The coupling is not depicted for clarity. Parameters set by the controller (550) can include rate control related parameters (picture skip, quantizer, lambda value of rate-distortion optimization techniques, . . . ), picture size, group of pictures (GOP) layout, maximum motion vector search range, and so forth. The controller (550) can be configured to have other suitable functions that pertain to the video encoder (503) optimized for a certain system design.

In some embodiments, the video encoder (503) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (530) (e.g., responsible for creating symbols, such as a symbol stream, based on an input picture to be coded, and a reference picture(s)), and a (local) decoder (533) embedded in the video encoder (503). The decoder (533) reconstructs the symbols to create the sample data in a similar manner as a (remote) decoder also would create (as any compression between symbols and coded video bitstream is lossless in the video compression technologies considered in the disclosed subject matter). The reconstructed sample stream (sample data) is input to the reference picture memory (534). As the decoding of a symbol stream leads to bit-exact results independent of decoder location (local or remote), the content in the reference picture memory (534) is also bit exact between the local encoder and remote encoder. In other words, the prediction part of an encoder “sees” as reference picture samples exactly the same sample values as a decoder would “see” when using prediction during decoding. This fundamental principle of reference picture synchronicity (and resulting drift, if synchronicity cannot be maintained, for example because of channel errors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a “remote” decoder, such as the video decoder (410), which has already been described in detail above in conjunction with FIG. 4. Briefly referring also to FIG. 4, however, as symbols are available and encoding/decoding of symbols to a coded video sequence by an entropy coder (545) and the parser (420) can be lossless, the entropy decoding parts of the video decoder (410), including the buffer memory (415) and the parser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decoder technology except the parsing/entropy decoding that is present in a decoder also necessarily needs to be present, in substantially identical functional form, in a corresponding encoder. For this reason, the disclosed subject matter focuses on decoder operation. The description of encoder technologies can be abbreviated as they are the inverse of the comprehensively described decoder technologies. Only in certain areas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may perform motion compensated predictive coding, which codes an input picture predictively with reference to one or more previously-coded picture from the video sequence that were designated as “reference pictures”. In this manner, the coding engine (532) codes differences between pixel blocks of an input picture and pixel blocks of reference picture(s) that may be selected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of pictures that may be designated as reference pictures, based on symbols created by the source coder (530). Operations of the coding engine (532) may advantageously be lossy processes. When the coded video data may be decoded at a video decoder (not shown in FIG. 5), the reconstructed video sequence typically may be a replica of the source video sequence with some errors. The local video decoder (533) replicates decoding processes that may be performed by the video decoder on reference pictures and may cause reconstructed reference pictures to be stored in the reference picture cache (534). In this manner, the video encoder (503) may store copies of reconstructed reference pictures locally that have common content as the reconstructed reference pictures that will be obtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the coding engine (532). That is, for a new picture to be coded, the predictor (535) may search the reference picture memory (534) for sample data (as candidate reference pixel blocks) or certain metadata such as reference picture motion vectors, block shapes, and so on, that may serve as an appropriate prediction reference for the new pictures. The predictor (535) may operate on a sample block-by-pixel block basis to find appropriate prediction references. In some cases, as determined by search results obtained by the predictor (535), an input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (534).

The controller (550) may manage coding operations of the source coder (530), including, for example, setting of parameters and subgroup parameters used for encoding the video data.

Output of all aforementioned functional units may be subjected to entropy coding in the entropy coder (545). The entropy coder (545) translates the symbols as generated by the various functional units into a coded video sequence, by lossless compressing the symbols according to technologies such as Huffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as created by the entropy coder (545) to prepare for transmission via a communication channel (560), which may be a hardware/software link to a storage device which would store the encoded video data. The transmitter (540) may merge coded video data from the video coder (503) with other data to be transmitted, for example, coded audio data and/or ancillary data streams (sources not shown).

The controller (550) may manage operation of the video encoder (503). During coding, the controller (550) may assign to each coded picture a certain coded picture type, which may affect the coding techniques that may be applied to the respective picture. For example, pictures often may be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decoded without using any other picture in the sequence as a source of prediction. Some video codecs allow for different types of intra pictures, including, for example Independent Decoder Refresh (“IDR”) Pictures. A person skilled in the art is aware of those variants of I pictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded and decoded using intra prediction or inter prediction using at most one motion vector and reference index to predict the sample values of each block.

A bi-directionally predictive picture (B Picture) may be one that may be coded and decoded using intra prediction or inter prediction using at most two motion vectors and reference indices to predict the sample values of each block. Similarly, multiple-predictive pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality of sample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 samples each) and coded on a block-by-block basis. Blocks may be coded predictively with reference to other (already coded) blocks as determined by the coding assignment applied to the blocks' respective pictures. For example, blocks of I pictures may be coded non-predictively or they may be coded predictively with reference to already coded blocks of the same picture (spatial prediction or intra prediction). Pixel blocks of P pictures may be coded predictively, via spatial prediction or via temporal prediction with reference to one previously coded reference picture. Blocks of B pictures may be coded predictively, via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to a predetermined video coding technology or standard, such as ITU-T Rec. H.265. In its operation, the video encoder (503) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancies in the input video sequence. The coded video data, therefore, may conform to a syntax specified by the video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional data with the encoded video. The source coder (530) may include such data as part of the coded video sequence. Additional data may comprise temporal/spatial/SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, and so on.

A video may be captured as a plurality of source pictures (video pictures) in a temporal sequence. Intra-picture prediction (often abbreviated to intra prediction) makes use of spatial correlation in a given picture, and inter-picture prediction makes uses of the (temporal or other) correlation between the pictures. In an example, a specific picture under encoding/decoding, which is referred to as a current picture, is partitioned into blocks. When a block in the current picture is similar to a reference block in a previously coded and still buffered reference picture in the video, the block in the current picture can be coded by a vector that is referred to as a motion vector. The motion vector points to the reference block in the reference picture, and can have a third dimension identifying the reference picture, in case multiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in the inter-picture prediction. According to the bi-prediction technique, two reference pictures, such as a first reference picture and a second reference picture that are both prior in decoding order to the current picture in the video (but may be in the past and future, respectively, in display order) are used. A block in the current picture can be coded by a first motion vector that points to a first reference block in the first reference picture, and a second motion vector that points to a second reference block in the second reference picture. The block can be predicted by a combination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-picture prediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such as inter-picture predictions and intra-picture predictions are performed in the unit of blocks. For example, according to the HEVC standard, a picture in a sequence of video pictures is partitioned into coding tree units (CTU) for compression, the CTUs in a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU includes three coding tree blocks (CTBs), which are one luma CTB and two chroma CTBs. Each CTU can be recursively quad-tree split into one or multiple coding units (CUs). For example, a CTU of 64×64 pixels can be split into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed to determine a prediction type for the CU, such as an inter prediction type or an intra prediction type. The CU is split into one or more prediction units (PUs) depending on the temporal and/or spatial predictability. Generally, each PU includes a luma prediction block (PB), and two chroma PBs. In an embodiment, a prediction operation in coding (encoding/decoding) is performed in the unit of a prediction block. Using a luma prediction block as an example of a prediction block, the prediction block includes a matrix of values (e.g., luma values) for pixels, such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to another embodiment of the disclosure. The video encoder (603) is configured to receive a processing block (e.g., a prediction block) of sample values within a current video picture in a sequence of video pictures, and encode the processing block into a coded picture that is part of a coded video sequence. In an example, the video encoder (603) is used in the place of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of sample values for a processing block, such as a prediction block of 8×8 samples, and the like. The video encoder (603) determines whether the processing block is best coded using intra mode, inter mode, or bi-prediction mode using, for example, rate-distortion optimization. When the processing block is to be coded in intra mode, the video encoder (603) may use an intra prediction technique to encode the processing block into the coded picture; and when the processing block is to be coded in inter mode or bi-prediction mode, the video encoder (603) may use an inter prediction or bi-prediction technique, respectively, to encode the processing block into the coded picture. In certain video coding technologies, merge mode can be an inter picture prediction submode where the motion vector is derived from one or more motion vector predictors without the benefit of a coded motion vector component outside the predictors. In certain other video coding technologies, a motion vector component applicable to the subject block may be present. In an example, the video encoder (603) includes other components, such as a mode decision module (not shown) to determine the mode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the inter encoder (630), an intra encoder (622), a residue calculator (623), a switch (626), a residue encoder (624), a general controller (621), and an entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of the current block (e.g., a processing block), compare the block to one or more reference blocks in reference pictures (e.g., blocks in previous pictures and later pictures), generate inter prediction information (e.g., description of redundant information according to inter encoding technique, motion vectors, merge mode information), and calculate inter prediction results (e.g., predicted block) based on the inter prediction information using any suitable technique. In some examples, the reference pictures are decoded reference pictures that are decoded based on the encoded video information.

The intra encoder (622) is configured to receive the samples of the current block (e.g., a processing block), in some cases compare the block to blocks already coded in the same picture, generate quantized coefficients after transform, and in some cases also intra prediction information (e.g., an intra prediction direction information according to one or more intra encoding techniques). In an example, the intra encoder (622) also calculates intra prediction results (e.g., predicted block) based on the intra prediction information and reference blocks in the same picture.

The general controller (621) is configured to determine general control data and control other components of the video encoder (603) based on the general control data. In an example, the general controller (621) determines the mode of the block, and provides a control signal to the switch (626) based on the mode. For example, when the mode is the intra mode, the general controller (621) controls the switch (626) to select the intra mode result for use by the residue calculator (623), and controls the entropy encoder (625) to select the intra prediction information and include the intra prediction information in the bitstream; and when the mode is the inter mode, the general controller (621) controls the switch (626) to select the inter prediction result for use by the residue calculator (623), and controls the entropy encoder (625) to select the inter prediction information and include the inter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference (residue data) between the received block and prediction results selected from the intra encoder (622) or the inter encoder (630). The residue encoder (624) is configured to operate based on the residue data to encode the residue data to generate the transform coefficients. In an example, the residue encoder (624) is configured to convert the residue data from a spatial domain to a frequency domain, and generate the transform coefficients. The transform coefficients are then subject to quantization processing to obtain quantized transform coefficients. In various embodiments, the video encoder (603) also includes a residue decoder (628). The residue decoder (628) is configured to perform inverse-transform, and generate the decoded residue data. The decoded residue data can be suitably used by the intra encoder (622) and the inter encoder (630). For example, the inter encoder (630) can generate decoded blocks based on the decoded residue data and inter prediction information, and the intra encoder (622) can generate decoded blocks based on the decoded residue data and the intra prediction information. The decoded blocks are suitably processed to generate decoded pictures and the decoded pictures can be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream to include the encoded block. The entropy encoder (625) is configured to include various information according to a suitable standard, such as the HEVC standard. In an example, the entropy encoder (625) is configured to include the general control data, the selected prediction information (e.g., intra prediction information or inter prediction information), the residue information, and other suitable information in the bitstream. Note that, according to the disclosed subject matter, when coding a block in the merge submode of either inter mode or bi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to another embodiment of the disclosure. The video decoder (710) is configured to receive coded pictures that are part of a coded video sequence, and decode the coded pictures to generate reconstructed pictures. In an example, the video decoder (710) is used in the place of the video decoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropy decoder (771), an inter decoder (780), a residue decoder (773), a reconstruction module (774), and an intra decoder (772) coupled together as shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from the coded picture, certain symbols that represent the syntax elements of which the coded picture is made up. Such symbols can include, for example, the mode in which a block is coded (such as, for example, intra mode, inter mode, bi-predicted mode, the latter two in merge submode or another submode), prediction information (such as, for example, intra prediction information or inter prediction information) that can identify certain sample or metadata that is used for prediction by the intra decoder (772) or the inter decoder (780), respectively, residual information in the form of, for example, quantized transform coefficients, and the like. In an example, when the prediction mode is inter or bi-predicted mode, the inter prediction information is provided to the inter decoder (780); and when the prediction type is the intra prediction type, the intra prediction information is provided to the intra decoder (772). The residual information can be subject to inverse quantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter prediction information, and generate inter prediction results based on the inter prediction information.

The intra decoder (772) is configured to receive the intra prediction information, and generate prediction results based on the intra prediction information.

The residue decoder (773) is configured to perform inverse quantization to extract de-quantized transform coefficients, and process the de-quantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residue decoder (773) may also require certain control information (to include the Quantizer Parameter (QP)), and that information may be provided by the entropy decoder (771) (data path not depicted as this may be low volume control information only).

The reconstruction module (774) is configured to combine, in the spatial domain, the residual as output by the residue decoder (773) and the prediction results (as output by the inter or intra prediction modules as the case may be) to form a reconstructed block, that may be part of the reconstructed picture, which in turn may be part of the reconstructed video. It is noted that other suitable operations, such as a deblocking operation and the like, can be performed to improve the visual quality.

It is noted that the video encoders (303), (503), and (603), and the video decoders (310), (410), and (710) can be implemented using any suitable technique. In an embodiment, the video encoders (303), (503), and (603), and the video decoders (310), (410), and (710) can be implemented using one or more integrated circuits. In another embodiment, the video encoders (303), (503), and (603), and the video decoders (310), (410), and (710) can be implemented using one or more processors that execute software instructions.

For a block that is coded in non-subblock mode, a motion vector predictor list can be constructed as follows: (1) candidate predictors from spatial and temporal neighboring blocks; (2) candidate predictors from HMVP buffer; (3) candidate predictors from a pairwise average of existing motion vector predictors; and (4) zero motion vector predictors using different reference pictures. Examples of these candidate predictors are described above.

When constructing the motion vector predictor list, a series of operations including an availability check and a redundancy check may be performed. The availability check checks whether a spatial or temporal neighboring block is coded in inter prediction mode. The redundancy check checks whether a new motion vector predictor is with a duplicate of any existing motion vector predictors in the motion vector predictor list. For example, an availability check and redundancy check is performed for the spatial and temporal candidates. The redundancy check is performed against existing candidates. Further, a redundancy check is performed, against the existing spatial/temporal candidates, for the candidates from the HMVP buffer. When the motion vector predictor list is long, these operations may require a number of cycles to execute. In a worst case, a picture is divided into many small blocks. The total number of cycles needed to complete the construction of motion vector predictor lists for all of these small blocks may be greater than a desirable value. For example, a merge candidate list for each coding block may not be the same as its neighboring blocks. Therefore, reducing the number of operations and simplifying the construction process of the motion vector predictor list is desirable, especially for the small blocks.

This disclosure presents improvement techniques for simplifying the construction process of the motion vector predictor list (e.g., in merge mode, skip mode, or AMVP mode) when certain block size constraints are met. That is, when a current block is considered as a small block, the construction process of the motion vector predictor list for the current block can be simplified such that a smaller number of motion vector predictors are included and/or fewer operations of an availability check and/or a redundancy check are performed.

Various thresholds can be used to indicate a small block. In an embodiment, when a block area of the current block is smaller than or equal to a threshold, the current block can be considered as a small block. In another embodiment, when the current block is to be further partitioned into a plurality of smaller blocks and one of the plurality of smaller blocks is smaller than or equal to the threshold, the current block is considered as a small block. The threshold can be a preset number of luma samples, such as 32 or 64 luma samples. The threshold can correspond to a picture resolution of the current picture. For example, for a picture with a large resolution, the threshold can be bigger compared to that for a picture with a small resolution. Further, the threshold can be signaled in a bitstream or coded video sequence, such as sequence parameter set (SPS), picture parameter set (PPS), slice or tile header, etc.

According to aspects of the disclosure, when the current block is considered as a small block, the construction process of the motion vector predictor list for the current block can be simplified such that a reduced number of motion vector predictors are included, as compared to a block that is not considered as a small block.

Motion vector prediction categories, such as spatial motion vector prediction, temporal motion vector prediction, and history-based motion vector prediction, etc., can each include a plurality of motion vector predictors. In an embodiment, when the current block is considered as a small block, the number of motion vector predictors from one or more of these categories can be reduced. For example, for each motion vector prediction category, a subset of the respective plurality of motion vector predictors is included into the motion vector predictor list, such that the motion vector predictor list is shorter compared to including all motion vector predictors into the list. The subset of motion vector predictors may be the first N (e.g., N=1, 2, etc.) candidates from each or some of the categories, where N is an integer number that is smaller than the number of possible candidates for the respective category. However, other predetermined candidates may be selected in other embodiments. The number N for each category, or some categories, may be the same or different. Further, the selection of the subset of motion vector predictors for each category, or some categories, may be the same or different. In one example, only the first N spatial and/or temporal candidates are allowed in the motion vector predictor list, where the number N is smaller than the number of possible spatial and temporal candidates. In some examples, N can be different for the spatial and temporal candidates.

In an embodiment, for the spatial motion vector prediction category and temporal motion vector prediction category, a subset of spatial motion vector predictors and a subset of temporal motion vector predictors are included in the motion vector predictor list, followed by HMVP candidates and others. In another embodiment, the motion vector predictor list does not include any spatial and/or temporal motion vector predictors. That is, no spatial and/or temporal candidates are allowed and the motion vector predictor list starts with HMVP candidates.

According to aspects of the disclosure, when the current block is considered as a small block, the construction process of the motion vector predictor list for the current block can be simplified such that fewer operations, such as redundancy check operations, are performed. The redundancy check compares a new motion vector predictor with any existing motion vector predictors in the motion vector predictor list.

In an embodiment, one or more redundancy checks between two spatial and/or temporal candidates can be removed. For example, the motion vector predictor list does not perform a redundancy check between a possible spatial motion vector predictor and an existing spatial motion vector predictor in the motion vector predictor list. In another example, the motion vector predictor list does not perform a redundancy check between a possible temporal motion vector predictor and an existing temporal motion vector predictor in the motion vector predictor list.

In an embodiment, one or more redundancy checks between a candidate from a HMVP buffer and existing candidates from spatial and/or temporal neighboring positions can be removed. For example, the motion vector predictor list does not perform a redundancy check between a possible history-based motion vector predictor and an existing spatial motion vector predictor in the motion vector predictor list. In another example, the motion vector predictor list does not perform a redundancy check between a possible history-based motion vector predictor and an existing temporal motion vector predictor in the motion vector predictor list.

In an embodiment, no redundancy checks are performed. That is, the motion vector predictor list is constructed without performing any redundancy check.

FIG. 8 shows a flowchart outlining an exemplary process (800) of simplifying the construction process of the motion vector predictor list according to some embodiments of the disclosure. In various embodiments, the process (800) is executed by processing circuitry, such as the processing circuitry in the terminal devices (210), (220), (230) and (240), the processing circuitry that performs functions of the video encoder (303), the processing circuitry that performs functions of the video decoder (310), the processing circuitry that performs functions of the video decoder (410), the processing circuitry that performs functions of the intra prediction module (452), the processing circuitry that performs functions of the video encoder (503), the processing circuitry that performs functions of the predictor (535), the processing circuitry that performs functions of the intra encoder (622), the processing circuitry that performs functions of the intra decoder (772), and the like. In some embodiments, the process (800) is implemented in software instructions, thus when the processing circuitry executes the software instructions, the processing circuitry performs the process (800).

The process (800) may generally start at step (S801), where the process (800) determines whether a current block is to be further partitioned. If the current block is determined not to be further partitioned, the process (800) will proceed to step (S802), otherwise the process (800) will proceed to step (S803).

At step (S802), the process (800) determines whether a block area of the current block is smaller than or equal to a threshold. If the block area of the current block is determined to be smaller than or equal to the threshold, the process (800) will proceed to step (S805), otherwise the process (800) will proceed to step (S806).

At step (S803), the process (800) partitions the current block into a plurality of smaller blocks and then proceeds to step (S804).

At step (S804), the process (800) determines whether a block area of one of the plurality of smaller blocks is smaller than or equal to the threshold. The threshold can be a preset number of luma samples, or can correspond to a picture resolution of the current picture, or can be signaled in the coded video sequence. If the block area of one of the plurality of smaller blocks is determined to be smaller than or equal to the threshold, the process (800) will proceed to step (S805), otherwise the process (800) will proceed to step (S806).

In some embodiments, step (S801) and/or step (S803) is optional and may not be performed. For example, if decoded prediction information of the current block indicates a partition size of the current block, the partition size indicates that the current block is to be further partitioned into a plurality of smaller blocks. The process (800) will determine whether the partition size is smaller than or equal to the threshold. This step is the same as step (S804). If the partition size is determined to be smaller than or equal to the threshold, the process (800) will proceed to step (S805), otherwise, the process will proceed to step (S806). In another embodiment, the comparison of the block with the threshold is performed after any block partitioning has already been performed.

At step (S805), the process (800) constructs a motion vector predictor list including a first number of motion vector predictors and then proceeds to step (S807).

At step (S806), the process (800) constructs the motion vector predictor list including a second number of motion vector predictors. The second number is larger than the first number. That is, the motion vector predictor list is simplified by reducing the second number of motion vector predictors to the first number of motion vector predictors, for example in the manner described above. Then the process (800) proceeds to step (S807).

At step (S807), the process (800) reconstructs the current block based on the motion vector predictor list. Then the process (800) terminates.

FIG. 9 shows a flowchart outlining an exemplary process (900) according to some embodiments of the disclosure. In various embodiments, the process (900) is executed by processing circuitry, such as the processing circuitry in the terminal devices (210), (220), (230) and (240), the processing circuitry that performs functions of the video encoder (303), the processing circuitry that performs functions of the video decoder (310), the processing circuitry that performs functions of the video decoder (410), the processing circuitry that performs functions of the intra prediction module (452), the processing circuitry that performs functions of the video encoder (503), the processing circuitry that performs functions of the predictor (535), the processing circuitry that performs functions of the intra encoder (622), the processing circuitry that performs functions of the intra decoder (772), and the like. In some embodiments, the process (900) is implemented in software instructions, thus when the processing circuitry executes the software instructions, the processing circuitry performs the process (900).

The process (900) may generally start at step (S901), where the process (900) decodes prediction information for a current block in a current picture that is a part of a coded video sequence. After decoding the prediction information, the process (900) proceeds to step (S902).

At step (S902), the process (900) determines whether an area of the current block is smaller than or equal to a threshold. Then process (900) proceeds to step (S903). The threshold can be a preset number of luma samples, such as 32 or 64 luma samples. The threshold can correspond to a picture resolution of the current picture. The threshold can be signaled in the coded video sequence.

At step (S903), the process (900) constructs a motion vector predictor list including a number of motion vector predictors. The number of motion vector predictors is based on whether the area of the current block is determined to be smaller than or equal to the threshold. In an embodiment, when the area of the current block is determined to be smaller than or equal to the threshold, the number of motion vector predictors included in the motion vector predictor list is a first number, otherwise, the number of motion vector predictors included in the motion vector predictor list is a second number that is larger than the first number.

In some embodiments, the prediction information indicates that the current block is to be further partitioned into a plurality of smaller blocks, the process (900) partitions the current block into a plurality of smaller blocks and determines whether an area of one of the plurality of smaller blocks is smaller than or equal to the threshold. The process (900) further constructs the motion vector predictor list based on whether the area of the one of the plurality of smaller blocks is determined to be smaller than or equal to the threshold. When the area of the one of the plurality of smaller blocks is determined to be smaller than or equal to the threshold, the number of motion vector predictors included in the motion vector predictor list is the first number; otherwise, the number of motion vector predictors included in the motion vector predictor list is the second number.

In some embodiments, the prediction information indicates a partition size of the current block. In such embodiments, the process (900) determines whether the partition size is smaller than or equal to the threshold. The process (900) further constructs the motion vector predictor list based on whether the partition size is determined to be smaller than or equal to the threshold. When the partition size is determined to be smaller than or equal to the threshold, the number of motion vector predictors included in the motion vector predictor list is the first number; otherwise, the number of motion vector predictors included in the motion vector predictor list is the second number.

In an embodiment, the motion vector predictor list including the first number of motion vector predictors is constructed based on a first set of spatial or temporal motion vector predictors. The first set of spatial or temporal motion vector predictors is smaller than a second set of spatial or temporal motion vector predictors used to construct the motion vector predictor list including the second number of motion vector predictors.

In an embodiment, the motion vector predictor list including the first number of motion vector predictors does not include any spatial or temporal motion vector predictors.

In an embodiment, a number of redundancy checks are reduced for construction of a motion vector predictor list that includes the first number of motion vector predictors. For example, a first number of redundancy checks is performed to construct the motion vector predictor list including the first number of motion vector predictors, and a second number of redundancy checks is performed to construct the motion vector predictor list including the second number of motion vector predictors. The first number of redundancy checks is less than the second number of redundancy checks.

In an embodiment, the first number of redundancy checks does not include at least one of a comparison between (i) a possible spatial motion vector predictor and a first existing spatial motion vector predictor in the motion vector predictor list, (ii) a possible temporal motion vector predictor and a first existing temporal motion vector predictor in the motion vector predictor list, (iii) a possible history-based motion vector predictor and the first or another existing spatial motion vector predictor in the motion vector predictor list, and (iv) the possible history-based motion vector predictor and the first or another existing temporal motion vector predictor in the motion vector predictor list.

In an embodiment, the motion vector predictor list including the first number of motion vector predictors is constructed without any redundancy check.

In an embodiment, at least one of the motion vector predictors uses the current picture as a reference picture such that a reference block of the at least one of the motion vector predictors is within the current picture.

At step (S904), the process (900) reconstructs the current block based on the motion vector predictor list.

After reconstructing the current block, the process (900) terminates.

While the embodiments above are based on reducing the number of redundancy checks in addition to the number of motion vector predictors, it is noted that the number of redundancy checks can be reduced without reducing the number of motion vector predictors in other embodiments.

A motion vector prediction method can use a different picture from the current picture as a reference picture. However, motion vector prediction or block compensation may be done from a previously reconstructed area within the current picture. Such motion vector prediction or block compensation may be referred to as intra picture block compensation, current picture referencing (CPR), or intra block copy (IBC). In the IBC prediction mode, a displacement vector that indicates an offset between a current block and a reference block within the current picture is referred to as a block vector (BV). The reference block is already reconstructed prior to the current block. It is noted that a BV can be considered as the MV discussed in this application.

The techniques described above, can be implemented as computer software using computer-readable instructions and physically stored in one or more computer-readable media. For example, FIG. 10 shows a computer system (1000) suitable for implementing certain embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code or computer language, that may be subject to assembly, compilation, linking, or like mechanisms to create code comprising instructions that can be executed directly, or through interpretation, micro-code execution, and the like, by one or more computer central processing units (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, internet of things devices, and the like.

The components shown in FIG. 10 for computer system (1000) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing embodiments of the present disclosure. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiment of a computer system (1000).

Computer system (1000) may include certain human interface input devices. Such a human interface input device may be responsive to input by one or more human users through, for example, tactile input (such as: keystrokes, swipes, data glove movements), audio input (such as: voice, clapping), visual input (such as: gestures), olfactory input (not depicted). The human interface devices can also be used to capture certain media not necessarily directly related to conscious input by a human, such as audio (such as: speech, music, ambient sound), images (such as: scanned images, photographic images obtain from a still image camera), video (such as two-dimensional video, three-dimensional video including stereoscopic video).

Input human interface devices may include one or more of (only one of each depicted): keyboard (1001), mouse (1002), trackpad (1003), touch screen (1010), data-glove (not shown), joystick (1005), microphone (1006), scanner (1007), camera (1008).

Computer system (1000) may also include certain human interface output devices. Such human interface output devices may be stimulating the senses of one or more human users through, for example, tactile output, sound, light, and smell/taste. Such human interface output devices may include tactile output devices (for example tactile feedback by the touch-screen (1010), data-glove (not shown), or joystick (1005), but there can also be tactile feedback devices that do not serve as input devices), audio output devices (such as: speakers (1009), headphones (not depicted)), visual output devices (such as screens (1010) to include CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch-screen input capability, each with or without tactile feedback capability—some of which may be capable to output two dimensional visual output or more than three dimensional output through means such as stereographic output; virtual-reality glasses (not depicted), holographic displays and smoke tanks (not depicted)), and printers (not depicted). These visual output devices (such as screens (1010)) can be connected to a system bus (1048) through a graphics adapter (1050).

Computer system (1000) can also include human accessible storage devices and their associated media such as optical media including CD/DVD ROM/RW (1020) with CD/DVD or the like media (1021), thumb-drive (1022), removable hard drive or solid state drive (1023), legacy magnetic media such as tape and floppy disc (not depicted), specialized ROM/ASIC/PLD based devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computer readable media” as used in connection with the presently disclosed subject matter does not encompass transmission media, carrier waves, or other transitory signals.

Computer system (1000) can also include a network interface (1054) to one or more communication networks (1055). The one or more communication networks (1055) can for example be wireless, wireline, optical. The one or more communication networks (1055) can further be local, wide-area, metropolitan, vehicular and industrial, real-time, delay-tolerant, and so on. Examples of the one or more communication networks (1055) include local area networks such as Ethernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TV wireline or wireless wide area digital networks to include cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial to include CANBus, and so forth. Certain networks commonly require external network interface adapters that attached to certain general purpose data ports or peripheral buses (1049) (such as, for example USB ports of the computer system (1000)); others are commonly integrated into the core of the computer system (1000) by attachment to a system bus as described below (for example Ethernet interface into a PC computer system or cellular network interface into a smartphone computer system). Using any of these networks, computer system (1000) can communicate with other entities. Such communication can be uni-directional, receive only (for example, broadcast TV), uni-directional send-only (for example CANbus to certain CANbus devices), or bi-directional, for example to other computer systems using local or wide area digital networks. Certain protocols and protocol stacks can be used on each of those networks and network interfaces as described above.

Aforementioned human interface devices, human-accessible storage devices, and network interfaces can be attached to a core (1040) of the computer system (1000).

The core (1040) can include one or more Central Processing Units (CPU) (1041), Graphics Processing Units (GPU) (1042), specialized programmable processing units in the form of Field Programmable Gate Areas (FPGA) (1043), hardware accelerators for certain tasks (1044), and so forth. These devices, along with Read-only memory (ROM) (1045), Random-access memory (1046), internal mass storage such as internal non-user accessible hard drives, SSDs, and the like (1047), may be connected through the system bus (1048). In some computer systems, the system bus (1048) can be accessible in the form of one or more physical plugs to enable extensions by additional CPUs, GPU, and the like. The peripheral devices can be attached either directly to the core's system bus (1048), or through a peripheral bus (1049). Architectures for a peripheral bus include PCI, USB, and the like.

CPUs (1041), GPUs (1042), FPGAs (1043), and accelerators (1044) can execute certain instructions that, in combination, can make up the aforementioned computer code. That computer code can be stored in ROM (1045) or RAM (1046). Transitional data can be also be stored in RAM (1046), whereas permanent data can be stored for example, in the internal mass storage (1047). Fast storage and retrieve to any of the memory devices can be enabled through the use of cache memory, that can be closely associated with one or more CPU (1041), GPU (1042), mass storage (1047), ROM (1045), RAM (1046), and the like.

The computer readable media can have computer code thereon for performing various computer-implemented operations. The media and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the kind well known and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system having architecture (1000), and specifically the core (1040) can provide functionality as a result of processor(s) (including CPUs, GPUs, FPGA, accelerators, and the like) executing software embodied in one or more tangible, computer-readable media. Such computer-readable media can be media associated with user-accessible mass storage as introduced above, as well as certain storage of the core (1040) that are of non-transitory nature, such as core-internal mass storage (1047) or ROM (1045). The software implementing various embodiments of the present disclosure can be stored in such devices and executed by core (1040). A computer-readable medium can include one or more memory devices or chips, according to particular needs. The software can cause the core (1040) and specifically the processors therein (including CPU, GPU, FPGA, and the like) to execute particular processes or particular parts of particular processes described herein, including defining data structures stored in RAM (1046) and modifying such data structures according to the processes defined by the software. In addition or as an alternative, the computer system can provide functionality as a result of logic hardwired or otherwise embodied in a circuit (for example: accelerator (1044)), which can operate in place of or together with software to execute particular processes or particular parts of particular processes described herein. Reference to software can encompass logic, and vice versa, where appropriate. Reference to a computer-readable media can encompass a circuit (such as an integrated circuit (IC)) storing software for execution, a circuit embodying logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents, which fall within the scope of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods which, although not explicitly shown or described herein, embody the principles of the disclosure and are thus within the spirit and scope thereof.

APPENDIX A: ACRONYMS AMVP: Advanced Motion Vector Prediction ASIC: Application-Specific Integrated Circuit BMS: Benchmark Set BS: Boundary Strength BV: Block Vector CANBus: Controller Area Network Bus CD: Compact Disc CPR: Current Picture Referencing CPUs: Central Processing Units CRT: Cathode Ray Tube CTBs: Coding Tree Blocks CTUs: Coding Tree Units CU: Coding Unit DPB: Decoder Picture Buffer DVD: Digital Video Disc FPGA: Field Programmable Gate Areas GOPs: Groups of Pictures GPUs: Graphics Processing Units

GSM: Global System for Mobile communications

HDR: High Dynamic Range HEVC: High Efficiency Video Coding HRD: Hypothetical Reference Decoder IBC: Intra Block Copy IC: Integrated Circuit JEM: Joint Exploration Model LAN: Local Area Network LCD: Liquid-Crystal Display LIC: Local Illumination Compensation LTE: Long-Term Evolution MR-SAD: Mean-Removed Sum of Absolute Difference MR-SATD: Mean-Removed Sum of Absolute Hadamard-Transformed Difference MV: Motion Vector OLED: Organic Light-Emitting Diode PBs: Prediction Blocks PCI: Peripheral Component Interconnect PLD: Programmable Logic Device PPS: Picture Parameter Set PUs: Prediction Units RAM: Random Access Memory ROM: Read-Only Memory SCC: Screen Content Coding SDR: Standard Dynamic Range SEI: Supplementary Enhancement Information SMVP: Spatial Motion Vector Predictor SNR: Signal Noise Ratio SPS: Sequence Parameter Set SSD: Solid-state Drive TMVP: Temporal Motion Vector Predictor TUs: Transform Units USB: Universal Serial Bus VUI: Video Usability Information VVC: Versatile Video Coding 

What is claimed is:
 1. A method for video decoding in a decoder, comprising: decoding prediction information for a current block in a current picture that is a part of a coded video sequence; determining whether an area of the current block is smaller than or equal to a threshold; constructing a motion vector predictor list including a number of motion vector predictors, the number of motion vector predictors being based on whether the area of the current block is determined to be smaller than or equal to the threshold; and reconstructing the current block based on the motion vector predictor list.
 2. The method of claim 1, wherein the number of motion vector predictors included in the motion vector predictor list is a first number when the area of the current block is determined to be smaller than or equal to the threshold, and the number of motion vector predictors included in the motion vector predictor list is a second number that is larger than the first number when the area of the current block is determined to be larger than the threshold.
 3. The method of claim 2, wherein when the prediction information indicates a partition size of the current block, the constructing further includes: constructing the motion vector predictor list based on whether the partition size is determined to be smaller than or equal to the threshold, wherein the number of motion vector predictors included in the motion vector predictor list is the first number when the partition size is determined to be smaller than or equal to the threshold, and the number of motion vector predictors included in the motion vector predictor list is the second number when the partition size is determined to be larger than the threshold.
 4. The method of claim 1, wherein the threshold is a preset number of luma samples.
 5. The method of claim 1, wherein the threshold corresponds to a picture resolution of the current picture.
 6. The method of claim 1, wherein the threshold is signaled in the coded video sequence.
 7. The method of claim 2, wherein the motion vector predictor list including the first number of motion vector predictors is constructed based on a first set of spatial or temporal motion vector predictors, the first set of spatial or temporal motion vector predictors being smaller than a second set of spatial or temporal motion vector predictors used to construct the motion vector predictor list including the second number of motion vector predictors.
 8. The method of claim 2, wherein the motion vector predictor list including the first number of motion vector predictors does not include any spatial or temporal motion vector predictors.
 9. The method of claim 2, wherein a first number of redundancy checks is performed to construct the motion vector predictor list including the first number of motion vector predictors, and a second number of redundancy checks is performed to construct the motion vector predictor list including the second number of motion vector predictors, the first number of redundancy checks being less than the second number of redundancy checks.
 10. The method of claim 9, wherein the first number of redundancy checks does not include at least one of a comparison between (i) a possible spatial motion vector predictor and a first existing spatial motion vector predictor in the motion vector predictor list, (ii) a possible temporal motion vector predictor and a first existing temporal motion vector predictor in the motion vector predictor list, (iii) a possible history-based motion vector predictor and the first or another existing spatial motion vector predictor in the motion vector predictor list, and (iv) the possible history-based motion vector predictor and the first or another existing temporal motion vector predictor in the motion vector predictor list.
 11. The method of claim 2, wherein the motion vector predictor list including the first number of motion vector predictors is constructed without any redundancy check.
 12. The method of claim 1, wherein at least one of the motion vector predictors uses the current picture as a reference picture.
 13. An apparatus for video decoding, comprising processing circuitry configured to: decode prediction information for a current block in a current picture that is a part of a coded video sequence; determine whether an area of the current block is smaller than or equal to a threshold; construct a motion vector predictor list including a number of motion vector predictors, the number of motion vector predictors being based on whether the area of the current block is determined to be smaller than or equal to the threshold; and reconstructing the current block based on the motion vector predictor list.
 14. The apparatus of claim 13, wherein the number of motion vector predictors included in the motion vector predictor list is a first number when the area of the current block is determined to be smaller than or equal to the threshold, and the number of motion vector predictors included in the motion vector predictor list is a second number that is larger than the first number when the area of the current block is determined to be larger than the threshold.
 15. The apparatus of claim 14, wherein the processing circuitry is further configured to: when the prediction information indicates a partition size of the current, construct the motion vector predictor list based on whether the partition size is determined to be smaller than or equal to the threshold, wherein the number of motion vector predictors included in the motion vector predictor list is the first number when the partition size is determined to be smaller than or equal to the threshold, and the number of motion vector predictors included in the motion vector predictor list is the second number when the partition size is determined to be larger than the threshold.
 16. The apparatus of claim 13, wherein the threshold is a preset number of luma samples.
 17. The apparatus of claim 13, wherein the threshold corresponds to a picture resolution of the current picture.
 18. The apparatus of claim 13, wherein the threshold is signaled in the coded video sequence.
 19. The apparatus of claim 14, wherein the motion vector predictor list including the first number of motion vector predictors is constructed based on a first set of spatial or temporal motion vector predictors, the first set of spatial or temporal motion vector predictors being smaller than a second set of spatial or temporal motion vector predictors used to construct the motion vector predictor list including the second number of motion vector predictors.
 20. A non-transitory computer-readable storage medium storing a program executable by at least one processor to perform: decoding prediction information for a current block in a current picture that is a part of a coded video sequence; determining whether an area of the current block is smaller than or equal to a threshold; constructing a motion vector predictor list including a number of motion vector predictors, the number of motion vector predictors being based on whether the area of the current block is determined to be smaller than or equal to the threshold; and reconstructing the current block based on the motion vector predictor list. 